Gripping and releasing apparatus and method

ABSTRACT

A passive universal gripper includes a mass of granular material encased in an elastic membrane. Using a combination of positive and negative pressure, the gripper can rapidly grip and release a wide range of objects that are typically challenging for conventional universal grippers, such as flat objects, soft objects, or objects with complex geometries. The gripper passively conforms to the shape of a target object, then vacuum-hardens to grip it rigidly; later using positive pressure to reverse this transition—releasing the object and returning to a deformable state. The apparatus and method enable the fast ejection of objects from the gripper, as well as essentially instantaneous reset time between releasing and gripping.

RELATED APPLICATION DATA

The instant application is a Divisional application of U.S. Ser. No.13/641,230 filed Dec. 21, 2012, which is a US National Phase filing ofInternational Application No. PCT/US11/32429 filed Apr. 14, 2011, whichclaimed priority to US Provisional application Ser. Nos. 61/436,688filed on Jan. 27, 2011 and 61/324,567 filed on Apr. 15, 2010, thesubject matter of all being incorporated herein by reference in theirentireties.

GOVERNMENT FUNDING

This invention was made with Government support under Project ID NumberW911NF-08-1-0140 awarded by DARPA. The United States Government hascertain rights in the invention.

BACKGROUND

1. Field of the Invention

Embodiments of the invention are in the field of robotics. Moreparticularly, embodiments of the invention pertain to passive-typeuniversal robot gripping and releasing apparatus and systems, associatedmethods, and applications thereof.

2. Related Art

Universal robot grippers are robotic end effectors that can grip a widevariety of arbitrarily-shaped objects. Proposed universal grippers haveranged from vacuum-based suction grippers to multi-fingered hands. Thesecan be divided into two categories: active universal grippers andpassive universal grippers.

Active universal grippers typically have an anthropomorphic,multi-fingered design, inspired by the human hand. Many such grippershave been developed, and multi-fingered grasping remains an active areaof research. The active universal grippers that have been proposed arecapable of both grasping and manipulation, but also engender extensivephysical and computational complexity, which is evident in graspalgorithm research. The complexities of active universal grippers,coupled with their correspondingly high costs, have limited theiradoption among commercial robotics industries.

Passive universal grippers, on the other hand, require minimal graspplanning. They are under actuated, and include components that passivelyconform to unique object geometries, giving them the ability to gripwidely varying objects without readjustment (see, e.g., P. B. Scott,“The ‘Omnigripper’: a form of robot universal gripper,” Robotica vol. 3,pp. 153-158, September 1985; R. Tella, J. Birk, and R. Kelley, “Acontour-adapting vacuum gripper,” Robot Grippers, D. T. Pham and W. B.Heginbotham, Eds. New York, N.Y.: Springer-Verlag, 1986, pp. 86-100; S.Hirose, “Connected differential mechanism and its applications,” RobotGrippers, D. T. Pham and W. B. Heginbotham, Eds. New York, N.Y.:Springer-Verlag, 1986, pp. 141-153; A. M. Dollar and R. D. Howe, “Arobust compliant grasper via shape deposition manufacturing,” IEEE/ASMETrans. Mechatron. vol. 11, pp. 154-161, April 2006). For example Scott,id., reported a gripper design in which many independent telescopingpins could each passively slide in or out to conform to the shape of atarget object, then pinch from the side to grip the object.

Passive universal grippers are generally simpler to use and requireminimal visual preprocessing of their environment, but they too have hadlimited success gaining widespread adoption. Often their many passivecomponents are easy to damage and difficult to replace. Passiveuniversal grippers can be very expensive as well, and their ability togrip many different objects often renders them inferior at gripping anyone object in particular.

One approach to achieving a lower threshold of universal gripping is toadd deformable materials to the gripping faces of a traditional jawedgripper in order to increase the compliance of the surfaces. Thistechnique is straightforward and can be sufficient for someapplications. Simpson (D. C. Simpson, “Gripping surfaces for artificialhands” Hand, Vol 3, pp. 12-14, February 1971) was likely the first tosuggest adding pockets of granular materials to gripping surfaces forthis purpose, and later Schmidt (I. Schmidt, “Flexible moulding jaws forgrippers,” Ind. Robot, vol. 5, pp. 24-26, March 1978) and Perovskii (A.P. Perovskii, “Universal grippers for industrial robots,” Rus. Eng. J.,vol 60, pp. 9-11, August 1980) proposed designs that allowed vacuumhardening of similar grain-filled pockets to produce a custom gripperjaw shape. Reinmueller and Weissmantel (T. Reinmuller and H.Weissmantel, “A shape adaptive gripper finger for robots,” Proc. Int.Symp. on Ind. Robots, April 1988, pp. 241-250), while presenting asimilar idea, went so far as to speculate that a single membrane filledwith granular material might be able to grip an object on its own andfunction as a passive universal gripper. However, this idea was notdemonstrated in practice or rigorously explored until the universaljamming gripper recently presented by us in E. Brown, N. Rodenberg, J.Amend, A. Mozeika, E. Steltz, M. Zakin, H. Lipson, H. Jaeger, “Universalrobotic gripper based on the jamming of granular material,” Proc. Natl.Acad. Sci., vol. 107, pp. 18809-18814, November 2010.

Passive, universal jamming grippers exploit the temperature independentfluid-like to solid-like pseudo-phase transition of granular materialsknown as jamming (see, e.g., T. S. Majmudar, M. Sperl, S. Luding, R. P.Behringer, “Jamming transition in granular systems,” Phys. Rev. Lett.,vol. 98, 058001, February 2007; A. J. Liu and S. R. Nagel, “Jamming isnot just cool any more,” Nature vol. 396, pp. 2122, November 1998; M. E.Cates, J. P. Wittmer, J. P. Bouchaud, and P. Claudin, “Jamming, forcechains, and fragile matter,” Phys. Rev. Lett., vol. 81, pp. 18411844,August 1998; A. J. Liu and S. R. Nagel, Jamming and rheology:constrained dynamics on microscopic and macroscopic scales, Taylor &Francis, London, 2001; C. S. O'Hern, L. E. Silbert, A. J. Liu, and S. R.Nagel, “Jamming at zero temperature and zero applied stress: the epitomeof disorder,” Phys. Rev. E, vol. 68, 011306, July 2003; E. I. Corwin, H.M. Jaeger, and S. R. Nagel “Structural signature of jamming in granularmedia,” Nature, vol. 435, pp. 10751078, April 2005). This type ofgripper leverages three possible gripping modes for operation: (a)static friction from surface contact, (b) geometric constraints fromcapture of the object by interlocking, and (c) vacuum suction when anairtight seal is achieved on some portion of the object's surface. Thesethree gripping modes are illustrated in FIG. 1. By achieving one or moreof these modes, the jamming gripper can grip many different objects withwidely varying shape, weight, and fragility, including objects that aretraditionally challenging for other universal grippers. For example wehave successfully been able to grip a coin, a tetrahedron, a hemisphere,a raw egg, a jack toy, and a foam earplug. The gripper functionsentirely in open loop, without grasp planning, vision, or sensoryfeedback.

When the gripped object is to be released, the gripper is vented toreturn to atmospheric (neutral) pressure and the object is let go. Theperformance of universal jamming grippers are limited by the need toreset the gripper between gripping tasks. An imprecise kneading ormassaging procedure is often necessary to return the gripper to aneutral state (i.e., manually resetting the gripper), or else itsability to grip subsequent objects rapidly degrades.

In view of the foregoing disadvantages, shortcomings, and problems knownin the art, the inventors have recognized the benefits and advantagesof, as well as the solutions provided by, an improved passive universalgripping apparatus, systems utilizing one or more passive universalgripping apparatus, associated methods, and applications and,particularly, such apparatus, systems, methods, and applications thatenable and utilize better object release, object ejection, and fasterreset time.

SUMMARY

An embodiment of the invention is a passive gripping and releasingapparatus that includes a deformable membrane having an openingfluidically coupled to a source of fluid ingress and egress in anevacuable sealing relationship; at least one port providing the sourceof fluid ingress and egress disposed in fluid connection with theopening of the membrane; and a granular material disposed within themembrane. According to various non-limiting aspects:

the granular material is characterized by having a volume change equalto or less than about 50% between a fluid phase and a solid phase of thematerial, more particularly, equal to or less than about 0.5%, and moreparticularly, equal to or less than about 0.05%;

the at least one port includes a fluid evacuation port and a fluid inputport;

the apparatus further includes a base disposed in coupling relation withthe membrane;

the apparatus further includes a filter disposed in coupling relationwith the opening of the membrane;

the apparatus further includes a pump coupled to the at least one port;

the pump is a reversible action pump;

the pump is internal to the apparatus;

the apparatus further includes a reservoir of compressed fluid coupledto the at least one port;

the apparatus further includes a collar disposed on the base andextending at least partially around a region of the membrane adjacentthe opening;

the membrane is made of a material that is flexible and evacuable;

the membrane may be made of any one of the following: vinyl, anelastomeric material, a coated cloth, a polyester film (e.g., Mylar), ametal foil, or particular combinations thereof;

the apparatus further includes a desiccant disposed within theapparatus;

the apparatus further includes means for reducing moisture within theapparatus;

the granular material disposed within the membrane may include small,individual solid granules or grains made from any type of metallic,insulating or semiconducting solid, including one or any combination ofone or more of plastic or polymeric particles, coffee grounds, cornstarch, ground glass, sand, rice, sawdust, crushed nut shells, oats,cornmeal, metal particles, dried ground corn husk, salt, seeds, groundrubber, rocks, and others known in the art;

the filling may include a granular material and a liquid;

the deformable membrane includes a plurality of independently controlledregions to which positive and negative fluid pressures can selectivelybe applied;

the independently controlled regions are self-contained and each includea granular material;

the apparatus further includes an internal membrane disposed internallyof the membrane, wherein the granular material includes a finer-grainedmaterial and the internal membrane includes a coarser-grained material.

An embodiment of the invention is a gripping and releasing device thatincludes more than one passive gripping and releasing apparatus, eachgripping and releasing apparatus further including a deformable membranehaving an opening fluidically coupled to a source of fluid ingress andegress in an evacuable sealing relationship; at least one port providingthe source of fluid ingress and egress disposed in fluid connection withthe opening of the membrane; and a granular material disposed within themembrane. According to various non-limiting aspects:

at least some of the deformable membranes have different sizes;

each of the passive gripping and releasing apparatus is coupled to acontrollable robotic arm.

An embodiment of the invention is a method for gripping and releasing anobject. The method includes the steps of providing a passive universaljamming gripper including a suitable jamming material characterized by afluid-like to solid-like phase transition upon application of a vacuum,wherein the gripper is in a gripped state in which an object is beinggripped; and applying a positive fluid pressure to the jamming materialto cause a solid-like to fluid-like phase transition, wherein thegripped object is actively released from the gripper. According tovarious non-limiting aspects:

the method further includes ejecting the gripped object by applying asufficient positive fluid pressure;

the method further includes gripping an object substantially immediatelyupon release of

the gripped object by contacting the object and applying a negativefluid pressure to the jamming material;

the method further includes alternating the positive and negative fluidpressure between releasing the gripped object and gripping the object;

the method further includes vibrating the gripper between releasing thegripped object and gripping the object;

the step of applying a positive fluid pressure further includes usingone of a gas and a liquid;

the gas is one of air, nitrogen, an inert gas.

According to various other non-limiting aspects of the apparatus andmethod:

the membrane will be flexible and will advantageously have a bendingstiffness ranging from approximately 1×10-5 Nm² to 1×10-4 Nm²;

the membrane should be impermeable to gas, such as air, so that apressure differential can be maintained across the membrane;

the membrane should resist cuts, tearing, rupturing, wear, chemicalinstability, or other physical failures, however, even latex membranes(ASTM cut level 0—the lowest cut level rating) have been successfullyused in prototypes. A durable membrane prolongs the life of the gripper,but is not necessary to achieve the gripping function;

membrane materials that provide a coefficient of static friction betweenthe membrane and the target object of greater than approximately 0.2 areparticularly advantageous, with higher coefficients offering improvedperformance;

membranes may, but need not be elastic. Elastic membranes with moduli inthe range of approximately 10 MPa to 100 MPa are advantageous;

membranes may have either a smooth or a textured surface, or acombination thereof. Smooth membrane surfaces help to induce the vacuumsuction gripping mode to the extent that they are able to maintain apressure differential when pressed against a smooth target objectsurface;

membranes may be somewhat sticky, and the level of stickiness can beoptimized for the application. Adhesion to steel ranging from 0 toapproximately 10 oz/in width (ASTM D-3330) have been shown to becompatible with a positive pressure gripper;

membrane thickness is determined by optimizing other characteristicssuch as flexiblilty, durability, toughness, friction coefficient, andsize of the gripper. There are no limits to the thickness range, andtypical membranes might have thicknesses from approximately 0.01 mm to 5mm. Thinner membranes generally conform better to details of objectgeometry, while thicker membranes are generally more robust;

composite material membranes may provide desirable performance, e.g., byincorporating the tear resistance of a cloth membrane with the frictionof an elastomeric coating. A composite material membrane is subject tothe same considerations as outline above;

In regard to gripper size ranges:

the jamming principle is scale independent; therefore, the upper size ofthe gripper membrane is only limited by weight and durabilityconsiderations;

there is no fundamental lower size gripper limit; however, additionalfactors such as size of the granular particles and membrane thicknessmay eventually limit ultimate miniaturization;

there is no fundamental upper or lower size limit on grippers of anyshape or arrayed in any combination;

In regard to granular material:

ideal grains flow well in the unjammed state and jam rigidly in thejammed state. A change in elastic modulus by a factor of 10 or larger isdesirable when crossing the jamming transition;

strings can be combined with grains, e.g., to produce a composite thathas high hardness and high bending stiffness;

In regard to fill density:

the quantity of grains used to fill the gripper membrane is governed bya tradeoff between trying to limit the free space inside the membraneand ensuring that the grains are loosely packed and can flow well in theunjammed state. Too much free space will cause the membrane to contracttoo much when the vacuum is applied, leading to a weak grip. Too littlefree space and the grains will not deform as well to the target object,also leading to a weak grip. In an aspect, ⅔ full, plus or minus a largerange was successful, and limiting fill density will depend on membraneelasticity and flexibility;

In regard to vacuum/positive pressure:

the range of vacuum required to achieve gripping depends on the jammingmaterial. For ground coffee in a latex balloon, for example,differential pressures larger than approximately 30 kPa (i.e., 70 kPabelow atmospheric pressure in situations where the outside of thegripper is at ambient conditions) are required to begin to achievesignificant gripping. The greater the pressure differential between theoutside and the inside of the membrane, the larger the gripping strengthwill be as all three gripping mechanisms scale directly with pressuredifferential;

the speed of jamming depends on the rate at which the air or other gasis removed from the membrane. Varying the jamming speed has littleinfluence on the grip performance;

objects held by the gripper are released when the vacuum within thegripper is released, allowing the granular material to unjam. Beyondreleasing the object, further unjamming is usually required before thegripper is reset enough to execute a subsequent grip. Positive pressureaccelerates the unjamming process by fluidizing the granular material,and can also impart additional force on the object to aid inejection—even to the point of shooting the object some distance;

the required flow rate into the gripper provided by positive pressure isdependent on the desired performance and the size of the gripper. Forshooting an object with an 8.5 cm diameter gripper, for example,positive flow rates between approximately 1 L/s and 10 L/s wererequired. Lower flow rates are required for smaller grippers and higherflow rates are required for larger grippers;

for resetting a gripper without ejecting an object, the volume of airflow into the gripper is more critical than the flow rate. The volumeinto the gripper should be approximately the same volume that wasextracted from the gripper during vacuum-hardening. Replacing thisvolume at higher flow rates will cause increased fluidization of thegrains, which is desirable;

neutralizing the pressure inside the gripper with the atmosphere(venting the gripper to atmosphere) is not necessary, but it simplifiesthe problem of pressure control by allowing the motion of the grains todictate some air flow. If the gripper is vented to atmosphere when it ispressed against an object, it can passively accept or reject air asnecessary to enable flow. A vent should advantageously resist this airflow as minimally as possible;

modulating the pressure within the gripper, e.g., oscillating betweenvacuum and positive pressure in the range of 1 Hz to 100 Hz, may be usedto encourage grains to flow around a target object as the gripper ispressed against the object;

vibration may be used to encourage grains to flow around a target objectas the gripper is pressed against the object. Possible methods forachieving these vibrations include: one or more motors with eccentricmasses, one or more piezoelectric elements, or electromagnetic actuatorsembedded in the granular material. Concerning the magnitudes andfrequency of vibration, accelerations ranging from below 1 g=9.8 m/s2 toseveral g can be used, with best frequency range from 10-100 Hz.

In regard to dehumidification or drying (important only for dry granularmaterial) fully submerged grains, i.e., the membrane is at leastpartially filled with grains and then water, may be advantageous;

moisture can decrease the ability of some grain materials to flow in theunjammed state. For these materials it is important to eliminate orminimize moisture within the system using desiccants, a dryer, adehumidifier, or closing the system to specific gases such as nitrogen;

the drying means or method may be located within the membrane among thegranular material (e.g., a desiccant), in the region of the filter,off-board of the gripper. Alternatively, desiccant grains can be mixedinto the granular material itself.

The embodied gripper apparatus incorporates a system for applyingpositive pressure to the granular material. Using a combination ofpositive and negative pressure, the gripper can rapidly grip and releasea wide range of objects that are typically challenging for conventionaluniversal grippers, such as flat objects, soft objects, or objects withcomplex geometries. The gripper passively conforms to the shape of atarget object, then vacuum-hardens to grip it rigidly, later usingpositive pressure to reverse this transition—releasing the object andreturning to a deformable state. By using both positive and negativepressure, the gripper's performance, reliability, and speed allincrease. The inventors have also demonstrated the fast ejection ofobjects from the gripper including launching a table tennis ball 50 cmvertically. In addition, multiple objects can be gripped and placed atonce while maintaining their relative distance and orientation.

Additional features and advantages of the invention will be set forth inthe detailed description which follows, and in part will be readilyapparent to those skilled in the art from that description or recognizedby practicing the invention as described herein, including the detaileddescription which follows, the claims, as well as the appended drawings.

It is to be understood that both the foregoing general description andthe following detailed description are merely exemplary of theinvention, and are intended to provide an overview or framework forunderstanding the nature and character of the invention as it isclaimed. The accompanying drawings are included to provide a furtherunderstanding of the invention, and are incorporated in and constitute apart of this specification. The drawings illustrate various embodimentsof the invention, and together with the description serve to explain theprinciples and operation of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic drawing illustrating how a jamming gripper canachieve three separate gripping modes: static friction from surfacecontact (left), geometric constraints from interlocking (center), andvacuum suction from an airtight seal (right), as known in the art;

FIG. 2 is an assembly drawing of a passive gripping and releasingapparatus, according to an exemplary embodiment of the invention;

FIG. 3 a is a photograph of the different size hemispheres used in atest of the embodied apparatus, ranging from 0.5 cm radius to 3.8 cmradius (left to right at top); and, FIG. 3 b is a diagram of theexperimental setup showing key dimensions. The apparatus picks theobject at the pick location (P₁) and then moves to place the object atthe place location (P₂). The contact angle between the gripper and theobject is indicated by θ;

FIG. 4 shows the results of gripping tests on hemispheres of differentradius using a manually reset gripping/release apparatus and anapparatus reset with positive pressure; (A) The success rate forgripping objects of varying size; (B) the force that the gripper appliesto an object while deforming around it; and (C) the contact angle thegripping/release apparatus achieves. The horizontal dotted line in (C)indicates the critical 45° contact angle;

FIG. 5 shows results from testing the embodied apparatus against errorsin the location of the target object. In (A), an error tolerance ofabout 3 cm as well as an increase in error tolerance of about 0.5 cm forthe positive pressure apparatus can be seen for a hemisphere of 2.47 cmradius. In (B), error tolerance and reliability can be seen moregenerally for errors ranging from 0 to 4.5 cm and hemispheres rangingfrom 0.45 to 3.72 cm radius using the unitless value [(e²+r²)^(1/2)]/R;

FIG. 6 is a bar graph showing comparative results for holding forcebetween positive pressure release and manual reset for 3D printedplastic shapes: helical spring, cylinder, cuboid, jack toy, cube,sphere, and regular tetrahedron. The sphere is 2.6 cm in diameter;

FIG. 7 shows placement test results for the calibration of the robotarm, test of the positive pressure gripper, and test of the manuallyreset gripper. Ellipses represent 95% confidence regions;

FIG. 8 shows a demonstration of throwing capability provided by apositive pressure apparatus, according to an illustrative aspect of theinvention. The positive pressure jamming apparatus is shown throwing atable tennis ball into a hoop in six time-stamped frames from a video;and

FIG. 9 shows nine starting configurations used to test the positivepressure jamming gripping/release apparatus's ability to grip multipleobjects at once, shown from a top view, according to an illustrativeaspect of the invention.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS OF THE INVENTION

In the following description, reference is made to the accompanyingdrawings that form a part hereof, and in which are shown by way ofillustration specific embodiments that may be practiced. Theseembodiments are described in sufficient detail to enable those skilledin the art to practice the invention, and it is to be understood thatother embodiments may be utilized and that structural, logical, andelectrical changes may be made without departing from the scope of thepresent invention. The following description of example embodiments is,therefore, not to be taken in a limited sense.

As used herein, the phrase “universal jamming gripper” means a passiveuniversal gripper as described in E. Brown, N. Rodenberg, J. Amend, A.Mozeika, E. Steltz, M. Zakin, H. Lipson, H. Jaeger, “Universal roboticgripper based on the jamming of granular material,” Proc. Natl. Acad.Sci., vol. 107, pp. 18809-18814, November 2010. In summary, a passiveuniversal gripper utilizes an elastic-type membrane (e.g., a balloon)that contains an amount of granular material (e.g., coffee grounds,sand, other). At atmospheric pressure, the granular material is in afluid-like phase such that it can flow, pour, or even splash. However,when a vacuum is applied, the granular material undergoes apseudo-jamming-phase transition into a solid-like phase, i.e., there isessentially no relative movement of a single grain with respect toanother. When the vacuum is released and the system returns toatmospheric pressure, the granular material will return to thefluid-like phase (either on its own over time or more quickly withexternal manipulation). This pseudo-phase transition arises out of theinherent solid-liquid duality of granular systems.

FIG. 2 illustrates a passive gripping and releasing apparatus 100. Theapparatus utilizes both positive and negative pressure so that once theapparatus has passively contacted an object to be gripped and conformedto the shape of the object, a vacuum can be applied to vacuum-harden thefilled membrane to rigidly grip the object and subsequently, one or morebursts of positive pressure are applied to reverse thefluid-like-to-solid-like phase transition (jamming), forcibly releasingthe object and returning (resetting) the filled membrane to adeformable, ready state.

In its simplest form, a jamming gripper needs only to include somegranular material contained in an evacuable membrane coupled to anegative pressure source in order to achieve its gripping behavior(e.g., the combination of ground coffee and a latex balloon has beenfound to work well (Brown et al., id.)), noting that no traditionalactuators are required, just an off-board pump to evacuate the air fromthe gripper. According to an exemplary aspect, the embodied passivegripping and releasing apparatus 100 shown in FIG. 2 includes a base 1(optional), an external collar 2 (optional), an elastic membrane 3 (e.g.latex balloon), granular filling material 4 (e.g., coffee grounds)within the membrane, an air filter 5 (optional), a vacuum line port 6, apositive pressure port 7, and an internal pump P (e.g., a reversibleroller pump; optional)). As shown, the membrane 3 is pinched between thebase 1 and the collar 2 producing an airtight (evacuable) seal. Othersealing apparatus and methods including but not limited to clamping,gluing, and others known in the art may also be effectively utilized. Inthis exemplary embodiment, the base and collar were manufactured from 3Dprinted plastic, which permits the intricate internal structures of thebase. The optional collar is an advantageous element of the design as ithelps guide the gripping/release apparatus as it conforms to an object,increasing the surface contact on vertical faces of the object andmaximizing the potential for the interlocking gripping mode. Theillustrated gripping/release apparatus can easily be interfaced to acommercial robot arm. The simple mechanical construction of the embodiedgripping/release apparatus 100 contributes to low cost and easymanufacturability.

A prototype gripping/release apparatus as embodied by apparatus 100 ofFIG. 2 included a latex balloon membrane that was pinched between thebase and the collar producing an airtight seal. The balloon membranethickness was 0.33 mm and it was filled with ground coffee beans to avolume of 350 cm³. At this volume the balloon membrane was full but themembrane was not significantly stretched, so the membrane could easilybe deformed in the unjammed state when contacted with an object. Thefilled membrane was nearly spherical, with a radius of approximately 4.3cm. The relatively low density of ground coffee was advantageous becauseit can be used in larger quantities without weighing down the apparatusor straining the membrane in the way that a heavier material like sandwould, for example.

It will be appreciated that various materials may effectively be usedfor the membrane element as long as they are substantially flexible andimpermeable to air (i.e., will hold a vacuum). Additional advantageousattributes of a membrane material include resistance to tearing (whichmay be obtained by the use of multiple layers of membrane material), andsome degree of stickiness or friction of the surface of the membrane.Non-limiting examples of membrane materials include elastomers, latex,vinyl, coated cloth, metal foil, Mylar, and others known in the art.

Various granular filling materials may also be utilized and materialswill advantageously undergo about a 5% or less change in volume over thefluid-like to solid-like pseudo-phase transition (jamming). It is alsoadvantageous that moisture in the system be substantially eliminated(i.e., when the fluid is not a liquid) as it slows the unjammingtransition due to additional capillary forces in the granular filling. Adesiccant may be used in the membrane and/or in the filter.Alternatively, a dry fluid such as nitrogen or an inert gas, forexample, could be used as the positive pressure fluid. An air dryingsystem as known in the art could also be attached to the air lines ofthe apparatus.

To demonstrate performance, the embodied gripping/release apparatus wasmounted on a commercial robot arm for testing. Positive pressure wasprovided by a pump at 620 kPa and a flow rate of 2.16 L/s. One or morefluid pressurized reservoirs could be used in place of or in combinationwith a positive pressure pump, which may enable a faster solid-like tofluid-like phase transition of the granular material. Vacuum wasachieved with an off board vacuum pump. A maximum vacuum flow rate of0.25 L/s was achieved with a pump rated for a maximum vacuum of 25microns. For gripping, the jamming transition was considered completewhen the pressure in the gripper dropped to −85 kPa, although usablevacuum pressures as high as −30 kPa were successfully used. The pressurein the gripping/release apparatus could also be neutralized with theatmosphere, and this state was used whenever the apparatus was pressedonto an object. Solenoid valves controlled by serial communicationthrough the robot arm were used to modulate the pressure in the gripper.All tests were performed at 100% joint angle speed for the robot arm,which corresponds to approximately 23.7 cm/s linear speed of thegripping/release apparatus.

The gripping/release apparatus was first evaluated for its reliabilityin gripping objects of varying size. All objects were located at aposition on a table that was hard-coded into the robot's software (thepick position). The robot was instructed to move to the pick positionand press the gripping/release apparatus onto an object, then actuatethe apparatus to induce the rigid state. Next, the robot was instructedto move to a place position, release the vacuum, and apply a short burstof positive pressure to eject the object. All tests were performed inopen loop.

In the past, spheres have been used for test objects for jamminggrippers, but spheres were not used for our test because the height of asphere grows at twice the rate of its radius. In a size test, this wouldquickly lead to a situation where the gripping/release apparatus baseand collar crash into larger spheres because the apparatus moves to thepick location in open loop. Instead, hemispheres were used (orientedflat side down) so that the surface geometry of a sphere test would bepreserved but the height of the test objects would be reduced. Woodenhemispheres ranging from 0.5 cm radius to 3.8 cm radius were chosen,with a surface texture that was not smooth enough to permit an airtightseal between the gripper membrane and the hemisphere, therefore notinducing the vacuum mode of gripping. Since the objects are hemispheres,it is also impossible to achieve the interlocking gripping mode in thistest. Each hemisphere was located in line with the central axis of thegripper, so that the contact angle θ would be as consistent as possiblearound the hemisphere. The test setup and the hemispheres used for thistest can be seen in FIG. 3. The dimensions associated with FIG. 3 wereas follows: h₁=4.8 cm, h₂=11.5 cm, h₃=13 cm, d=20 cm.

Test results are shown in FIG. 4. The ordinate of each plot is presentedas a percentage of the membrane size in order to account for thescalability of the gripping/release apparatus. FIG. 4 shows theperformance of the embodied positive pressure gripping/release apparatuscompared to a passive universal gripper that must be manually reset bythe user. Plots of success rate, applied force, and contact angle areshown. Success rate was determined over 30 trials for each hemisphereand represents how reliably the apparatus could grip hemispheres ofvarying size. Applied force is the force that a gripper applies to anobject as it is deformed around it. This force is measured with a scalelocated beneath the test object. Contact angle is the maximum angle atwhich the gripper membrane and the object touch (indicated by θ in FIG.3). For the applied force and contact angle tests, ten trials wereperformed on each hemisphere. For all three plots the data pointsrepresent the average of the trials, and the error bars indicate themaximum and minimum measurements recorded during the test. Hemisphereswere tested in random order for all tests.

It can be seen that for a passive universal gripper not utilizingpositive pressure, the gripper's success rate falls off sharply as theobject radius reaches about 65% of the membrane radius, and falls to 0%for contact angles near 45° (the critical angle for gripping to occur).No minimum object radius was observed in this test, though nohemispheres under 5 mm radius were tested due to their lack ofavailability in wood. We also see that the applied force increases withincreasing object size, as more grains inside the membrane need to bedisplaced around larger objects. Adding positive pressure dramaticallyincreases the success rate of the gripping/release apparatus by as muchas 85% for some hemispheres by increasing contact angle. Positivepressure also decreases the force applied to the object by as much as90%. These performance increases are most likely due to increasedfluidization of the granular material, which allows it to flow moreeasily around the target object.

In a second test, the embodied gripping/release apparatus was evaluatedfor tolerance to errors in the location of the target object. The sametest setup from FIG. 3 was used, with hemispheres again employed as testobjects. In this test, however, the target object was located between 0and 4.5 cm away from the pick location P₁, thus causing the hemisphereto be unaligned with the central axis of the gripping/release apparatus.Results from this test are shown in FIG. 5. In FIG. 5A, only results forthe 2.47 cm radius hemisphere are shown, and thirty trials wereperformed for each data point. FIG. 5B illustrates a more generalrelationship between target object size, location error, and grippingsuccess rate, and ten trials were performed for each data point shown,with errors ranging from 0 to 4.5 cm and hemispheres ranging from 0.45to 3.72 cm radius.

FIG. 5A could be redrawn for any of the hemispheres we tested and asimilar improvement for the positive pressure gripping/release apparatuswould be shown. However, we find that the expression [(e²+r²)^(1/2)]/Rallows us to observe the error tolerance and reliability of theapparatus more generally. This expression can be understood as theEuclidean distance from the apex of the target object to the point wherethe membrane touches the table along its central axis, compared with theradius of the membrane. It is a simple approximation for the totalsurface area the membrane will contact (table plus target object) as itattempts to wrap around the object to the critical contact angle,compared with the available surface area of the membrane. An analyticalcalculation of these two surface areas would likely produce a moreaccurate quantity, but such a calculation is prohibitively difficult dueto the deformation and stretching of the membrane that occurs during thegripping process. We see in FIG. 5B that our approximation issufficiently simple and accurate to collapse the data and allow forquick estimations of gripping success rate. In addition, the closesimilarity between FIG. 4A and FIG. 5B should be noted. This result isexpected because [(e²+r²)^(1/2)]/R reduces to r/R for e=0.

The error tolerance we observe for the embodied apparatus is very largeconsidering its open loop function. In FIG. 5A, for example, we see thatwith the use of positive pressure our 3.5 cm radius membrane cansuccessfully pick up a 2.47 cm radius hemisphere 100% of the time, evenwhen the hemisphere is 2.5 cm away from its target location. It islikely that this large error tolerance would prove very useful forgripping tasks in unstructured environments where precise control overneither the situation nor the robot is possible.

In a third test, the positive pressure gripping/release apparatus wasevaluated for the range of shapes that it could grip, and the forceswith which it could retain those shapes. Seven shapes with similar mass,volume, and size were 3D printed for the test. The mass of each shapewas 15.5 g±0.8 g. The minimum cross section of each shape wasapproximately 2.6 cm, a size chosen to be well within the 100% successrate from the previous test. The 3D printed material is not smoothenough for an airtight seal to be achieved. The shapes printed were:helical spring, cylinder, cuboid, jack toy, cube, sphere, and regulartetrahedron. A photograph of the shapes is shown on the ordinate of FIG.6. To test the strength with which each object was retained, we measuredthe force required to pull each object out of the solidified (evacuated)membrane. The results of this test are shown in FIG. 6. Ten tests wereperformed for each shape, and the error bars indicate the maximum andminimum measurements recorded during the tests.

It can be seen that resetting the apparatus with positive pressureimproves the holding force for objects that displace a larger volume ofgrains in the membrane, but decreases the holding force for smallerobjects. This may be understood as a tradeoff between contact angle andapplied force in the experimental setup. The enhanced flowability of thepositive pressure apparatus allows for a larger contact angle as seen inFIG. 4C, and thus an enhanced holding force for the larger objects thatdisplace a larger volume of grains. However, a problem occurs for thesmaller objects which do not displace a large volume of grains. Forthese smaller objects, no significant increase in contact angle occurs,and instead the enhanced flowability may allow more grains to fall tothe side of the object, possibly leaving a gap between the grains andthe apparatus base. This is supported by the low values of applied forcein FIG. 4B for the positive pressure apparatus, which are comparable tothe weight of the grains for small objects. In this situation, when themembrane is evacuated, the grains may partially contract toward the openspace near the base rather than toward the target object, resulting inless holding force. This is not an inherent problem with the positivepressure modification, as it could be fixed by applying more force tothe target object, either by sensing the pick height to the targetobject size, or by using a robot arm with force feedback.

For the test setup in FIG. 3, a maximum gripping rate can be calculated.The limiting factors are the maximum speed of the robot arm, the timerequired to complete the jamming transition, the time required to resetthe gripper between grips, and the time required to release the grippedobject. The maximum speed of the robot arm was measured at 23.7 cm/s,which limits the maximum grip rate to 24 picks/min for the time requiredsimply to move from P₁ to P₂ and back again. We consider the jammingtransition complete when the pressure inside the membrane has dropped to−85 kPa, which takes 1.1 s for our 350 cm³ membrane—this further limitsthe maximum gripping rate down to 16.7 picks/min.

A positive pressure jamming gripping/release apparatus requires only 0.1s to release the object and reset the gripper with a single burst ofpositive pressure, which limits the maximum gripping rate finally to16.2 picks/min. For a manually reset gripper, releasing the object andresetting the gripper is a bit more complicated. The time required torelease an object depends on the geometry of the object, and slowerrelease times limit the gripping rate. We measured the slowest releasetimes at 0.6 s. Manually resetting the gripper requires the operator toperform an imprecise kneading or massaging routine, which took at least2.0 s during our testing. Thus for a manually reset passive universalgripper, the maximum gripping rate is limited to 10.2 picks/min. Thebenefit of including positive pressure then is a 39% increase ingripping rate, in addition to the benefits of increased automation ofthe system and the elimination of possible human error when resettingthe gripper.

Typically, placement accuracy is recognized as a sacrifice that must bemade when developing a passive universal gripper in order to maximizethe range of objects that may be gripped. However, placement accuracy isalso a key performance measure for grippers used in manufacturingsettings. Here, the embodied jamming gripping/release apparatus isevaluated for the accuracy with which it can place objects, again usingthe same test setup from FIG. 3 with slight modifications.

We first performed a calibration procedure to determine the accuracy ofthe robot arm itself. A pen was firmly mounted to the wrist of therobot, extending to approximately the same point at which the membrane'sbottom edge makes contact with the table. A similar test procedure toFIG. 3 was then executed, with the pen marking a fixed piece of paper atthe pick and place positions P₁ and P₂. With this setup, we were able todetermine the precision of the arm to be ±0.35 mm in the worst case for95% confidence, with an average offset of 0.76 mm from the goal. Thisresult is an order of magnitude larger than the manufacturer's reportedrepeatability of ±0.05 mm, which is likely due to the dynamic effectscaused by moving the robot arm at full speed.

Next, the pen was removed from the robot arm and the apparatus wasreattached. The robot arm was programmed to execute a pick and placeroutine with the hemisphere, again using the test setup from FIG. 3.Following placement of the hemisphere, we were able to measure itsdeviation from its intended position in the plane of the table. In thistest, only the 1.82 cm radius hemisphere was used. This hemisphere issimilar to the part sizes used in the shape test and is well within the100% success rate range in the reliability test. The dimensions of FIG.3 were modified slightly for this test to maximize placement accuracy:when testing the positive pressure gripper, h₂ was set at 8.8 cm, andwhen testing the manually reset gripper, h₂ was set at 7.1 cm. Theresults are shown in FIG. 7.

We see from FIG. 7 that the positive pressure apparatus places thehemisphere more accurately than the manually reset gripper, while themanually reset gripper is slightly more precise. Specifically, theaverage deviation of the positive pressure apparatus is 0.98 mm from thearm's calibration center, with a precision of +1.00 mm in the worst casefor 95% confidence, while the average deviation for the manually resetgripper is 2.63 mm from the arm's calibration center, with a precisionof +0.76 mm in the worst case for 95% confidence.

The angular placement accuracy of the two grippers was comparable. Herehowever, the manually reset gripper was slightly more accurate, whilethe positive pressure apparatus was slightly more precise. The manuallyreset gripper rotated the hemisphere by 5.4° on average, +3.4° for 95%confidence. The positive pressure apparatus rotated the hemisphere by7.5° on average, ±1.8° for 95% confidence.

The placement accuracy improvement that we observe for the positivepressure jamming apparatus enables the repeatable shooting behaviorshown in FIG. 8, which shows the embodied positive pressure apparatusthrowing a table tennis ball into a hoop in six time-stamped frames froma video. Our preliminary testing finds that the shooting behavior isrepeatable.

A unique feature of passive universal jamming grippers is their abilityto grip multiple closely spaced objects simultaneously while maintainingtheir relative position and orientation. To quantify this capability weused two cuboids as test parts, each 1.3×1.3×4.5 cm. Thegripping/release apparatus was evaluated for picking these objects atthe nine starting configurations shown in FIG. 9. For each test thecentroid of the combined shape was located on the central axis of themembrane. The relative distance and angle between the two objects wasrecorded before and after the gripping operation.

We found that for relative distance, the manually reset gripper tendedto increase the separation between the objects by 0.08 cm on average±0.86 cm for 95% confidence, while the embodied positive pressureapparatus tended to increase the separation between the objects by 0.77cm on average ±1.07 cm for 95% confidence. In terms of relative angle,the manually reset gripper changed the angle between the objects by 6.7°on average, ±20.5° for 95% confidence, while the embodied positivepressure apparatus changed the angle between the objects by 5.2° onaverage, ±22.2° for 95% confidence.

This test shows a significant decrease in accuracy from the previoustest where only one object was used. The increase in error is likely theresult of grips that occur away from the central axis of the membrane,where off-axis forces that tend to rotate or translate the grippedobjects are more likely to occur. The performance of the embodiedpositive pressure apparatus is slightly inferior to the manually resetgripper in this test, presumably because the rapid expansion of themembrane during the ejection of the object magnifies these off axisforces, producing increased rotations and translations of the grippedobjects. This test reveals the importance of centering objects on thegripper's central axis in order to maximize placement accuracy.

The performance of both the embodied positive pressure apparatus and themanually reset gripper in this test indicates that they can be used togrip multiple objects at once, but that their ability to maintain therelative distance and angle between the objects is only suitable fortasks where a lower degree of accuracy is required. For example, thiscapability may be useful for transferring multiple aligned parts priorto a more accurate assembly operation.

We have disclosed a passive, universal, jamming, gripping and releasingapparatus that incorporates both positive and negative pressure. Thedesign and manufacture of an exemplary prototype were described, andthis prototype was evaluated against five metrics that revealed itscapabilities for real-world applications. The apparatus proved capableat gripping objects of different size and shape, and showed an increasein reliability of up to 85%, an increase in tolerance for errors in thetarget object location, and an increase in speed of 39% over a manualreset a passive, universal, jamming gripper. The positive pressureapparatus also applied up to 90% less force on target objects, anddemonstrated an increase in placement accuracy, which enabled a newthrowing capability for the gripper. This ability to throw objects maybe useful for tasks like, but not limited to, sorting objects into binsin a factory or throwing away trash in a home.

The embodied apparatus enables objects of very different shape, weight,and fragility to be gripped, and multiple objects can be gripped at oncewhile maintaining their relative distance and orientation. Thisdiversity of abilities may make the apparatus well suited for use inunstructured domains ranging from military environments to the home. Theapparatus's airtight construction also provides the potential for use inwet or volatile environments and permits easy cleaning. Its thermallimits are determined only by the membrane material due to thetemperature independence of the jamming phase transition, so use inhigh- or low-temperature environments may be possible. Further, the softmalleable state that the membrane assumes between gripping/releasingtasks could provide an improvement in safety when deployed in closeproximity with humans, as in the home, for example.

All references, including publications, patent applications and patentscited herein are hereby incorporated by reference to the same extent asif each reference were individually and specifically indicated to beincorporated by reference and were set forth in its entirety herein.

The use of the terms “a” and “an” and “the” and similar referents in thecontext of describing the invention (especially in the context of thefollowing claims) are to be construed to cover both the singular and theplural, unless otherwise indicated herein or clearly contradicted bycontext. The terms “comprising,” “having,” “including,” and “containing”are to be construed as open-ended terms (i.e., meaning “including, butnot limited to,”) unless otherwise noted. The term “connected” is to beconstrued as partly or wholly contained within, attached to, or joinedtogether, even if there is something intervening.

The recitation of ranges of values herein are merely intended to serveas a shorthand method of referring individually to each separate valuefalling within the range, unless otherwise indicated herein, and eachseparate value is incorporated into the specification as if it wereindividually recited herein.

All methods described herein can be performed in any suitable orderunless otherwise indicated herein or otherwise clearly contradicted bycontext. The use of any and all examples, or exemplary language (e.g.,“such as”) provided herein, is intended merely to better illuminateembodiments of the invention and does not impose a limitation on thescope of the invention unless otherwise claimed.

No language in the specification should be construed as indicating anynon-claimed element as essential to the practice of the invention.

It will be apparent to those skilled in the art that variousmodifications and variations can be made to the present inventionwithout departing from the spirit and scope of the invention. There isno intention to limit the invention to the specific form or formsdisclosed, but on the contrary, the intention is to cover allmodifications, alternative constructions, and equivalents falling withinthe spirit and scope of the invention, as defined in the appendedclaims. Thus, it is intended that the present invention cover themodifications and variations of this invention provided they come withinthe scope of the appended claims and their equivalents.

We claim:
 1. A method for operating a universal gripping and releasingapparatus, comprising: providing a universal gripping and releasingapparatus, comprising: a deformable membrane having an openingfluidically coupled to a positive source of fluid ingress and a negativesource of fluid egress in an evacuable sealing relationship, wherein thepositive source of fluid ingress is above atmospheric pressure; at leastone port providing the source of fluid ingress and egress disposed influid connection with the opening of the membrane; and a granular,jamming material characterized by a fluid-like to solid-like phasetransition upon application of one of a negative fluid pressure and avacuum, disposed within the membrane; and applying at least one of apositive fluid pressure that is above atmospheric pressure to thejamming material to cause a solid-like to fluid-like phase transition ofthe jamming material and a negative fluid pressure that is less thanatmospheric pressure to the jamming material to cause a fluid-like tosolid-like phase transition of the jamming material.
 2. The method ofclaim 1, further comprising: contacting an object with the gripping andreleasing apparatus when the jamming material is in a fluid-like phase;applying a negative fluid pressure that is less than atmosphericpressure to the jamming material to cause the fluid-like phase totransition to a solid-like phase and gripping the object; and applying apositive fluid pressure that is greater than atmospheric pressure to thejamming material to cause the solid-like phase to transition to thefluid-like phase and releasing the gripped object.
 3. The method ofclaim 1, further comprising: contacting an object with the gripping andreleasing apparatus when the jamming material is in a fluid-like phase;applying a negative fluid pressure that is less than atmosphericpressure to the jamming material to cause the fluid-like phase totransition to a solid-like phase and gripping the object; and applying asufficient positive fluid pressure that is greater than atmosphericpressure to the jamming material to cause the solid-like phase totransition to the fluid-like phase and forcibly releasing the grippedobject.
 4. The method of claim 2, further comprising gripping anotherobject upon release of the originally gripped object by contacting theanother object and applying a negative fluid pressure that is less thanatmospheric pressure to the jamming material to cause the fluid-likephase to transition to a solid-like phase and gripping the anotherobject.
 5. The method of claim 4, further comprising releasing theanother gripped object.
 6. The method of claim 4, further comprisingforcibly releasing the another gripped object.
 7. The method of claim 1,further comprising venting the membrane to the atmosphere when it iscontacting the object.
 8. The method of claim 2, further comprisingalternating the positive and negative fluid pressure between releasingthe gripped object and gripping the object.
 9. The method of claim 2,further comprising vibrating the gripping and releasing apparatusbetween releasing the gripped object and gripping the object.
 10. Themethod of claim 1, wherein the step of applying a positive fluidpressure further comprises using one of a gas and a liquid.
 11. Themethod of claim 10, wherein the gas is one of air, nitrogen, an inertgas.
 12. The method of claim 1, further comprising creating a volumechange in the granular material that is equal to or less than about 5%between a fluid phase and a solid phase of the material.
 13. The methodof claim 1, further comprising independently controlling regions of thedeformable membrane to which the positive and negative fluid pressuresare selectively applied.
 14. The method of claim 2, further comprising:further applying a positive fluid pressure that is greater thanatmospheric pressure to the jamming material during or after contactingthe object with the gripping and releasing apparatus when the jammingmaterial is in a fluid-like phase to further conform the deformablemembrane to the object prior to applying the negative fluid pressurethat is less than atmospheric pressure to the jamming material to causethe fluid-like phase to transition to a solid-like phase and grippingthe object.
 15. A method of operating a universal gripping and releasingapparatus, comprising: positioning the apparatus to contact an object,the apparatus comprising: a deformable membrane having an openingconfigured to be fluidically coupled to a positive source of fluidingress and a negative source of fluid egress in an evacuable sealingrelationship, wherein the positive source of fluid ingress is aboveatmospheric pressure; at least one port providing the source of fluidingress and egress disposed in fluid connection with the opening of themembrane; and a granular, jamming material characterized by a fluid-liketo solid-like phase transition upon application of one of a negativefluid pressure and a vacuum, disposed within the membrane; and applyingat least one of a positive fluid pressure that is above atmosphericpressure to the jamming material to cause a solid-like to fluid-likephase transition of the jamming material and a negative fluid pressurethat is less than atmospheric pressure to the jamming material to causea fluid-like to solid-like phase transition of the jamming material. 16.A method of operating a universal gripping and releasing apparatus,comprising: positioning the apparatus to contact an object, theapparatus comprising: a deformable membrane having an opening configuredto be fluidically coupled to a positive source of fluid ingress and anegative source of fluid egress in an evacuable sealing relationship; atleast one port providing the source of fluid ingress and egress disposedin fluid connection with the opening of the membrane; and a granularmaterial disposed within the membrane, configured to undergo afluid-like to solid-like phase transition upon application of one of anegative fluid pressure and a vacuum; gripping the object by applying anegative fluid pressure that is less than atmospheric pressure to thejamming material to cause a fluid-like to solid-like phase transition ofthe jamming material; and releasing the object by applying at least oneof a positive fluid pressure that is above atmospheric pressure to thejamming material to cause a solid-like to fluid-like phase transition ofthe jamming material.